454 Glossary
concentrations in a biochemical system or voltages and currents in
an electronic system. A source vertex is a vertex with only directed
branches leaving it. A sink vertex has no directed branches leaving it.
vertex distance (in graph theory): See distance.
volt-ampere: AC power measure. A volt-ampere is a vector quantity, having
a real and imaginary part. VAR stands for volt-ampere reactive, the
imaginary component of a generator’s load, for instance. For max-
imum generator efciency, it is desired to minimize a generator’s
VAR output. The real power supplied from a generator is P = VI cosφ
watts, where VI is the output volt-amperes, and φ is the phase angle
between output voltage V and current I. P is obviously maximum
when ...